The present invention relates to a simultaneous voice and data communications system using telephone stations and data terminal equipments, with possibility of connection to public or private networks.
Business communication systems have undergone an evolution which, starting from electromechanical systems with voice communication services, have developed to advanced systems, providing an integral solution to the communications requirements in office automation.
The first systems to be considered when analyzing the generic problem of communication in offices, are those fundamentally concerning voice switching. These systems in almost all cases have adopted one of the following configurations:
(1) PABX
This solution copies the architecture, and in many cases the equipment of public telephone exchanges and makes use of them to comply with the requirements of private organizations.
The PABX's have the following characteristics:
The centralized configuration which they use is a cause of high fixed costs, which can only be compensated by the installation of a high number of subscribers. However they are optimum when the number of subscribers is very large. PA0 The installation is quite rigid as it is made by means of line pairs asigned to each subscriber. Modifications of the configuration require changes implying service interruptions, and also specialized personnel. PA0 They are intended for voice services. Data services are included at high cost, and with bandwidth limitations in analogic exchanges. Digital PABX's pretend to offer access to data services in a more easy way. PA0 Normally they offer a wide range of net facilities (abbreviated selection, access to closed groups, etc.) They seldom offer the possibility of connection of multifeature telephones. PA0 The PABX's fundamentally are connected to the switched public telephone network. Normally they do not provide access to public or private data networks. PA0 Most of them are electromechanical and their normal structure is as a multiwire bus from which the individual terminals are connected. They are, in general, of small capacity, and whithin this range, they become more economical than a PABX. PA0 Normally they are systems provided with blocking as the bus usually provides fewer circuits than connected terminals. PA0 The installation is rigid, in as much as the location of the terminals on the bus is not easily modificable. Thus normally a physical modification of the equipment is required, and consequently, the system must be taken out of service placement to achieve the modification. PA0 They do not include data services. PA0 Normally they only provide the facilities peculiar to these type of systems, such as: complete signaling of all positions, transfer facilities, multi-operator, etc., but do not include extra facilities, (directory, agenda, etc.) PA0 Normally they are connected to the public switched telephone network or to a PABX. PA0 Very wide connectability range, from very few, to hundreds or thousands of terminals. There are diverse architectures, topologies (ring, bus, star) and mechanisms of access (protocols). In general, they often are more costly than the equivalent voice systems. PA0 Usually they are systems employing blocking with a statistical use of the available bandwidth, even during connection. PA0 They usually are very flexible systems, in their installation, and reconfiguration, particularly as compared with conventional data systems. PA0 They are not intended for voice handling, due to the statistical nature of information transfers. PA0 They provide a wide range of data services and facilities including added value functions, that increase the capabilities of the basic service. PA0 The range of terminal devices connected, depends on the manufacturer, but in general, it is very wide. PA0 They are normally connected to public data networks, or otherwise to other terminal devices associated wtih public switched telephone networks by means of vocal band modems. PA0 It is a simultaneous voice and data communications system, with possibility of connection to public or private networks. The system is completely modular, and the cost depends exclusively on the number of equipped stations. It may be applied to large offices, by adding interconnected systems. PA0 The system provides a flexible installation which is easy to connect, and reconfigure. PA0 The system provides simultaneous voice and data services. The interfacing and protocols required for data service do not penalize the telephone service. PA0 The system provides a wide range of voice facilities. In addition to having all of the characteristics of a key system, it offers a user "friendly" mode of operation that guides a user through a host of system features such as abbreviated dialing, agenda, directory, clock, etc. PA0 The connection of a data terminal is simple and flexible. The protocols and formats satisfy the requirements of the present market (RS 232-C, BSC, SDLC, etc.). If the user so requires, additional feature modules may be added. PA0 The hardware is universal, and its adaptation depends on the software. PA0 The system may be connected to the following networks:
(2) Key Systems
In those cases in which the number of telephone sets does not justify the cost of a PABX, where the functions of a telephone operator must be shared by several subscriber's positions, or when it is desired to simplify access, both internal and external, and provide more complete signaling the normally offered solutions are within the key system category. Key systems have the following characteristics.
These systems are fundamentally intended for voice switching and have a long record in the office communication systems market.
Recently, local area networks have been developed. The notion of a local area network (LAN) has become popular for several reasons. The most evident reason being the suitability of providing a mechanism to allow equipment from different manufacturers, to be inter-connected through a common communication media. In this way, mini-processors, terminals, personal computers, text processors, mass memory devices, printers, etc, can be linked.
At the present moment, basically, there are two protocols for local area networks defined by the 802 Commision of the IEEE. The first of them is the CSMA/CD (Carrier Sense Multiple Access/Collision Detection). The first is a packet broadcast system based on Ethernet (industry standard proposed by Digital Equipment, Intel, and Zerox). The second is the "Token Passing" system supported by IBM. However, none of these protocols have been designed for an efficient and economic handling of voice signals. Local area networks have the following general characteristics: